Catching Right Time For Diactyl Rest?

ON my first Lager. Everything is going very well. It's day 7, and my airlock is bubbling at about once very 5-7 seconds, so it has slowed.

From everything I've read, I want to do a Diactyl rest at 10 degrees higher than my fermentation temp 10 days after intial fermentation or when the fermentation has slowed.

From what I gathered, do you have to catch it at that exact timeframe? If you say do the Rest after fermentation is done, or too soon, will this have any effect? I hope my train of thought is clear.......

Time is never a good predictor for fermentation completion. Too many variables, and thus impossible to predict when to do a D-rest. The best way is to do as you have and notice when fermentation has slowed a little. Then take gravity readings until you reach about 75% of fermentation. That's when I raise the temp by 10F.